Variable inductor



Feb. 11, 1936. R. M. HEINTZ 2,030,369

VARIABLE INDUCTOR Filed April 17, 1934 INVENTOR RALPH M. HE/NTZ.

BY A

A TTO NEYS Patented Feb. 11, 1936 UNITED STATES PATENT OFFICE- Claims. (c1. 111-242) ILv invention relates to variable inductors adapted for use inradio transmitting or receiving provide a variable inductor in which the inductor itself is non-rotatable: and to provide an improved construction and a more efiicient methodfor varying the inductance of coils.

Other objects of my invention will be apparent or will be specifically pointed out in the description forminga part of this specification, but I do not limit myself to the embodiment of the invention herein described, as various forms may be adopted within the scope oi the claims.

Referring to the drawing:

Figure 1 is a sectional elevation of apparatus my invention.

Figure 2 is a fragmental cross sectional view of the inductor. The plane in which the view is taken is indicated by the line 2-2of Figure 1.

Figure 3 is a ditic view of a typical circuit incorporating the variable inductor of my invention.

In broad tenns,-my invention comprises an inductor having a plurality of helically disposed electrically conductive turns, and provided with means for supporting it in a fixed position. An electrically conductive guide is provided, disposed adjacent to, and preferably coaxiaily with, the inductor, said guide having threads thereon which correspond in pitch with the pitch of the turns of the inductor. 'A resilient conductive link, having one end thereof engaged in a thread of the guide, and the other end thereof in slidable contact with a turn of the inductor, is provided for electrically connecting the two elements; and means are provided for rotating the link about the inductor to cause the end of the link contacting the turn thereof to follow a helical path corresponding with the helix of the turns thereof.

Inductors used in the tuned circuits of high frequency radio transmitters and receivers are generally provided with vernier mechanisms whereby the number of turns of the inductance in the circuit. or the location of a tap, may be varied. Heretofore it has been the practice to provide a rotatable inductor. having the desired number of helically disposed turns. and provided with a lead screw which permitted the inductor s to be advanced past a fixed contact, a distance corresponding with thelead ofthehelix ofthe inductor for each revolution thereof.

It is obvious that, due to the combined rotary and axial movement of the inductor, coiled pig- 1o tails. or collector rings and brushes, must necessarilybeusedtopermitconnectionoftheinductor with other fixed parts of the apparatus. The inclusion of these pigtails in low frequency circuits, where the inductor is provided with a large number of turns, is not detrimental, but in high frequency apparatus where the inductor has only a few turns, the effect of the pigtails is quite pronounced in varying the overall inductance of the coil between terminals. due to vibration go which changes the inductance of the pigtails and due to the erratic behavior of the pigtail in not returning to the same value of inductance for successive settings of the inductor proper. It willbeseemthereforethattheuseofanindig5 eating device, such as a dial, with an inductor of this character is impractical due to'the fact that the dial would not give a true evaluation of the setting of the inductor. Furthermore, the inductance of the connections may possibly be so greater than the inductance of the coil.

I have provided a variable inductor in which pigtails, or like flexible means for connecting the inductor to fixed parts of the apparatus, are eliminated, and one which permits the use of a as dial therewith which will give a true indication of the value of inductance included in a circuit.

In greater detail, the variable inductor of my invention preferably comprises a'cylindrical insulating form 2 having a helical groove I formed 40 thereon for increasing the electrical leakage distance between the turns oi an inductance 4 disposed thereon. The form 2 is provided with a closed end t having a metallic bushing I mounted thereon which is adapted to receive the reduced end 8 of a cylindrical stud 9. A nut II is provided, threaded on the stud end I, for the purpose of securing the form 2 to the stud, and to provide means for connecting the stud with one end of the inductance 4. through the medium of a lead It. A lead It is secured to the other end 0! the inductance to which other parts of the transmitting or receiving apparatus may be connected. The stud l is provided with a threaded end it which is screwed into a suitable fixed member, so

whichmaybaforexamplathepanel ildfthe apparatus.

Aninsulatingdisk i'lisprovidedhavinga bushing II which functionawhentheend It of conductive link II is provided having at one end thereof a straight portion 22 which is adapted to bear against adjacent ridges II of the threads I. and which is also provided with a pin on which aroller ",spacedsiightLvfromthe bottomofthe threads and adapted to roll on the side walls thereof, is iournalled. The other end of the link is provided with an inturned portion 21 contacting the inductance I, the edge of which is curved to conform with the periphery of the inductance.

Thisiinkservutoelectricallyconnecttheinductance and the guide II. the latter being provided with a terminal II, the lead I. from which maybe connected with other parts of the ap- The close proximity of the short circuited loop, created by the tubular guide II, to the inductance 4 would not materially affect the inductance when the latter is used in receiving circuits; however, when it is used in transmitting circuits the eddy current'losses caused thereby would be considerable. To eliminate this difliculty I prefer to provide the guide It with two or more slots 8. which extend from the edge of the guide to points adjacent the flange 2|. Thus the flange is the closest closed loop to the inductance fleld and it is spaced therefrom a distance which will not permit any appreciable coupling between the two parts. The purpose of the plurality of slots in the guide is to preclude any possibility of the roller 2| bridging the slot and short circuiting the loop formed by the guide if but one slot was provided.

Means are provided for rotating the link about theinductancesoastovarythevalueof the latter. Rotatably mounted on the stud Q is a sleeve 3| which has, at one end thereof, a flange 82 to which an insulating arm 33 may be connected by means of the screw 34. The'arm is provided with a hollow guide block ll secured thereto, through which the link Ii passes. The bent portion II of the link is adapted to bear against the inner face of the guide block so as to compress the link and cause the ends thereof to press against the guide II and the turn of inductance with which it happens to be in contact. The other end of the sleeve II is provided with a gear I. and a pinion 3! carried by a shaft ll, journaled in the panel ll, meshes therewith. Indicating means such as a dial 4! may be secured to the end of the shaft 4|.

In operation. the dial 4! is turned, which also rotates the pinion II. This rotation is imparted to the sleeve 3|, through the gear 38, and consequently the arm II, guide block II and the link II are rotated together. As the link 2i rotates, the roller II will follow the thread It with the result tnat the link is advanced longitudinally at each revolution a distance corresponding with the pitch of the thread, which in this case corresponds with the pitch of the helix of the inductance. By continued rotation of the dial l2,theportion2| ofthellnkiscausedtofollow theturns dftheinductancaincontacttherewith.

fromoneendthereoftotheother. Itisunder stood that stops, not shown, may be provided either on the inductance or on the guide I. for limiting the travel of the link.

Flgure3illustratesatypicalcircuitusingthe variable inductor of my invention. This may be considered as a portion of a radio transmitter in which the vacuum tube 48 represents the output tube. The inductor l is shown as being shunted acrosstheanodellandground lltowhichthe cathode 41 is connected by the lead 0. A variable tuning condenser ll is shunted across the inductanceandtheguidellisshownasbeing connected withthe antenna ll. Tuningmaybe accomplished eitherbyvaryingthecondenserll, or the inductor l. or both. The circuit may be read as a receiving circuit by considering that the inductorisconnectedto thegridilandthat the anode It is connected to the radio frequency amplifler of the receiver.

In reiteration, the variable inductor just described possesses marked superiority over the types of variable inductors in present use, by reason of the fewer number of relatively movable current carrying parts contained therein; by reason of the absence of coiled pigtails with their attendant undesirable featiu'es, and by virtue of its sturdier and simplifled mechanical construction.

It willbe understoodthattheproportionsof themechanismshowninthedrawingwere chosen for illustrative purposes, and that these proportions, such as the diameter, number of turns, and length of the inductance, and the sizes of other parts of the'apparatus, may be varied within wide limits without departing from the spirit of the invention.

' I claim: v

l. A variable inductor comprising a fixed helical inductance, a flxed coaxial guide spaced axially from said inductance and having threads thereoncorrespondinginpitchtotheturnsof said helix,acontactlinkdisposedparallelwith the axes of the inductance and the guide and having one end touching said inductance and the other end entering said threads, and means for rotating said link around said inductance and guide. 1

2. A variable inductor comprising a flx ed helical inductance, a flxed conductive guide cylinder having external threads thereon corresponding in pitch with the turns of said inductance. said guide cylinder being substantially of the same diameter as said inductance and mounted coaxially therewith and spaced apart therefrom, a flexible contact link having one end in contact withaturn ofsaidhelical inductanceandthe other end entering said threads, and means rotating around the common axis for directing said link around said guide andsaid inductance.

3. In combination with a support, a stud fastened to said support, a flxed conductive drum fastenedv to said stud by an insulating member, said drum having guide threads cut on the external surface thereof, a fixed insulating frame fastened to said stud of the same diameter as said drum, and coaxial therewith, said drum and said frame being spaced apart, a helix mounted on said frame having the same pitch as the threads on said drum, a sleeve mounted on said stud between said drums and said frame, an arm on said sleeve extending radially between said drumandsaid frame,alinkchannelin said arm, aspringlinkpassingfreely throughsaidclnnnel having one end contacting a turn of said helix and the other end engaging said threads, said link being deformed by said channel to exert pressure on said threads and said turn, and means for rotating said sleeve.

4. A variable inductor comprising a fixed helical inductance, a fixed coaxial guide spaced apart from said inductance and having threads thereon corresponding in pitch with the turns of said Inductance, a contact link having one end thereof in contact with a turn of said inductance and the other end thereof in engagement with a thread of said guide, and means movably connected with said link between the point of contact thereof with said inductance and the point of engagement thereof with said guide for moving said link about said inductance.

5. A variable inductor comprising a fixed helical inductance, an arm having a sleeve thereon mounted for rotary movement about the axis of said inductance, means for rotating said arm and sleeve. a contact link slidabiy positioned in said sleeve and having one end thereof in contact with a turn of said inductance. said link lying in a position in axial parallelism with the axis of said inductance, and means connected to the opposite end of said link for advancing. when said arm and sleeve are rotated. the end of said link in contact with said inductance, about said inductance in contact therewith.

6. A variable inductor comprising a fixed helical inductance, a fixed cylindrical guide disposed in axial alinement with said inductance and spaced axially therefrom, said guide comprising a plurality of arcuate radially disposed spaced sections, said sections each having co-extensive portions of a screw thread formed thereon corresponding in pitch with the pitch of the turns of said inductance, a contact link having one end thereof engaging a turn of said inductance and the other end thereof in engagement with said screw thread, and means for rotating said con- 2 

